a) Field of the Invention
The invention is directed to an arrangement for generating radiation by means of a gas discharge containing a discharge chamber, which has a discharge area for the gas discharge for forming a plasma that emits the radiation from a starting material and an emission opening for the generated radiation, a first electrode and a second electrode which are mounted so as to be rotatable, and a high-voltage power supply for generating high-voltage pulses between the two electrodes.
b) Description of the Related Art
Radiation sources which are based on plasmas generated by gas discharge and which rely on various concepts have already been described many times. The principle common to these arrangements consists in that a pulsed high-current discharge of more than 10 kA is ignited in a gas of determinate density, and a very hot (kT>20 eV) and dense plasma is generated locally as a result of the magnetic forces and the dissipated power in the ionized gas.
It is particularly important to prolong the life of the source components because exchanging them causes downtimes in production facilities in which the radiation sources are employed.
In radiation sources based on a gas discharge, it is principally the electrode system, in particular the electrodes, that is subject to extensive wear caused by heating and erosion. While the heating of the electrodes is brought about chiefly by the flow of current through the electrodes and by the radiation of the plasma, fast particles exiting from the radiation-emitting plasma lead to erosion.
Known solutions corresponding to WO 2005/025280 A2 and RU 2 252 496 C2 use rotating electrodes in order to counter the heating of the electrodes.
In the arrangement disclosed in WO 2005/025280 A2 which is suitable for metal emitters, the rotating electrodes also dip into a vessel containing molten metal, e.g., tin, wherein the metal applied to the electrode surface is vaporized by laser radiation, and the vapor is ignited by a gas discharge to form a plasma.
WO 2005/025280 A2 further proposes conveying the current pulse to the electrodes by means of the molten metal in that the capacitors needed for storing the electrical energy for plasma generation are electrically connected to the liquid metal in the vessels by means of a plurality of metal pins or bands which are embedded in a vacuum-tight manner in insulators. Since the capacitors are arranged outside of the discharge chamber, this inevitably leads to a high inductance in the discharge circuit due to the required current feedthroughs to the electrodes. This lengthens the duration of the current pulses through the electrodes so that the energy that can be deposited in the plasma cannot be used efficiently for generation of radiation.